Automatic control system for aircraft



April 1948. R; H. QNISBET ET AL 2,439,750

AUTOMATIC CONTROL SYSTEM FOR AIRCRAFT Filed Sept. 17, 1942 v s Sheets-Sheet 1 INVENTORS,

R0 T H. NISBET, and

BER ARTHUR H G EN NY 7 TH flATTORNEY.

April 13, 1948 R. H. NISBET m. 2,439,750

AUTOMATIC CONTROL SYSTEM FOR AIRCRAFT Filed Sept. 17, 1 42 s Sheets-Sheet 2 INVENTO ROBERT H. NlSB and THEIR ATTORN Y.

Ap 1948. R. H. NISBET El AL. 2,439,750

AUTOMATIC CONTROL SYSTEM FOR AIRCRAFT Filed Sept. 17, 1942 3 Sheets-Sheet'3 INVENTORS ROBERT H. NISBET AND RT UR NY 'ATT R EY.

Patented Apr. 13, 1948 AUTOMATIC CONTROL SYSTEM FOR AIRCRAFT Robert Hayes Nisbet, Stroud, and Arthur Philip Glenny, Amberley, England, assignors to The Sperry Gyroscope Company, Limited, Brenford, England, a British company Application September 17, 1942, Serial No. 458,654 In Great Britain November 22, 1940 Section 1, Public Law 690, August 8, 1946 Patent expires November 22, 1960 20 Claims. 1

This invention relates to automatic control systems for aircraft. More particularly it relates to the control of aircraft equipped not only with the usual manual control but also with a so-called automatic pilot for normal automatic control comprising means responsive to changes of course, and to changes of attitude and/or speed, of the craft, and servo-motors and relays whereby the control surfaces of the craft are automatically actuated to control the craft. The problem dealt with by the present invention is that of emergency control to prevent the aircraft from crashing if the pilot loses consciousness during a high speed manoeuvre, or is killed as a result of enemy action, or is otherwise mentally or physically incapacitated, Such emergencies may arise during a turn or other manoeuvre of the aircraft at an instant at which the aircraft is banked, or is climbing or diving, at a steep angle, and while it is perhaps at a low altitude; and there is therefore a considerable danger that, as a result, the craft may crash before anyone on board can take over the controls-from the pilot.

In order to overcome the above mentioned danger the present invention provides an emergency automatic control for aircraft available in conjunction with the usual alternative manual and/or automatic pilot control system, and includes continuously actin means urging automatic change-over from manual to emergency automatic control and positively held out of operation or over-controlled by the pilot during manual control. The automatic controlling mechanism set into action during emergency automatic control is desirably Wholly or in part that embodied in the automatic pilot but the control initiating means for emergency automatic control about at least one axis of the craft includes a controlling device other than the primary control instrument of the automatic pilot. This emergency controlling device exerts control over the craft through the servo-motors and relays of the automatic pilot which may be of any standard type, e. g. one of the automatic pilots described in United States Patents Nos. 1,992,970, 2,210,916, 2,210,917, 2,310,954 and application S. N. 259,178, filed March 1, 1939, now Patent No. 2,432,504.

The continuously acting means urging automatic change-over from manual to emergency automatic control involve only a light continuously acting force such as a light spring easily overcome by the pilot during manual control and quite apart from the forces involved in the actual automatic actuation of the control surfaces.

Preferably the Way in which the pilot during manual control holds the continuously acting means out of operation is by the act of grasping the control wheel, so that, if he releases his grasp of the control wheel, the emergency automatic control automatically takes over control of the aircraft. Preferably, also, an alarm is arranged to indicate When the emergency control is in operation.

There are several reasons why it is desirable to use a controlling device for emergency control of the craft about at least one axis thereof other than the control instrument of the normal automatic pilot.

In the first place as regards azimuth control, at the instant when emergency control is brought into operation, the craft may not be flying in the direction previously set on the automatic pilot; consequently, if the normal automatic control were put into operation, the aircraft would be set into a turn. perhaps at a high rate of turn, towards the heading previously set. This might well be dangerous. We therefore arrange that during the emergency control conditions the rudder at least is not controlled from the normal rudder-controlling instrument, e. g. the directional gyroscope of the normal automatic pilot, but is brought to a central, or nearly central position. For this purpose the rudder may, under emergency control conditions, be freed from all control so that it will find its own position of balance, but we prefer to arrange that the emergency control positively drives the rudder to its central position. To obtain this result the relay controlling the rudder servo-motor is no longer controlled from the directional gyroscope, but solely from means responsive to the position of the rudder, or to the presstue acting on the rudder, so that, whenever the rudder is not central, the servo-motor is actuated in the appropriate direction to drive the rudder towards the central position.

In the second place, as regards control of inclination of the craft, the provision of a primary controlling device other than the instrument used in normal automatic pilot control is desirable for emergency automatic control for the following reason. In a normal automatic pilot system the ailerons and usually also the elevator are controlled from delicate and sensitive gyroscopic instruments, e, g. from a gyro-vertical. However, such yroscopic instruments are not usually designed to operate when the aircraft is inclined at a large angle, and during abnormal manoeuvres the instruments are usually either caged or otherwise put out of action; if not, the gyroscopes may be precessed to entirely erroneouspositions, and perhaps even damaged, dueto their striking against stops that limit their angular movement relative to the craft, or else due to forced precession as a result of movements of the craft when the gyrosoopes have lost precession freedon due to a change in the position of the gimbal axes. If this should have happened,the gyroscope can no longer be relied on to maintain level flight. We therefore arrange that, 'atleast-in cases where the aircraft may have been inclined at large angles, the ailerons are controlled, under the emergency control according to theinvention, from an alternative rugged and coarse controlling instrument which may be .a pendulum, or the equivalent, instead of from a delicate and sensitive gyroscopic instrument, the control being arranged to keep the aircraft horizontal about the fore-and-aft axis. This has the advantage that the control instrument used in emergency control is not liable to become displaced as a result of manoeuvres carried out by the craft that may have involved large inclination angles and thus to define an incorrect attitude for the craft if the emergency control system is subsequently brought into operation. Similarly the elevator may be controlled from an alternativecontrolling instrument which may be a pendulum or an airspeed responsive device. If control of the elevator from a pendulum is adopted, the control is arranged to keep the aircraft flying substantially horizontally, while, if control from an air-speed indicator is adopted, this is arranged to adjust the attitude of the craft so as to maintain a predetermined air-speed, as suggested in the prior patent to Elmer A. Sperry, No. 1,368,226, dated February 8, 1929, for Aeroplane stabilizers.

The pendulum controllers for the bank and climb axes may be of any known type responsive to gravity; for example, they may be liquid pendulums; or they may be rollers, or other equivalents of a pendulum. Their movements relative to the craft or to their casings may be damped by viscous damping devices and they may be provided with auxiliary spring constraints'centralising them to the craft or to their casings,

A form of pendulum controller particularly suitable for use in the invention is hereinafter described. It comprises an inverted or overslung pendulum mounted with a limited and small amount of freedom of movement relative to a member connected to the aircraft. Such a controller has the disadvantage that it has no position of rest and must therefore produce continuous small oscillations in the craft that it controls. However, it has no natural period of its own with which disturbances or oscillations of the craft can resonate, and it is very sensitive, the slightest deflection from the vertical position being sufficient to cause the pendulum to move to the full extent of the movement permitted by the stops. It is particularly suited to electrical control of the contacting type, as it moves more vigorously into contact with the co-operating contacts and rests with greater pressure against them than does a positive pendulum. When it is 'used in conjunction with a pneumatic control these ports then "cushions the impactand' prevents' the pendulumfrom rebounding, while it sirable that the movements of a control surface (the ailerons or the elevator), brought about by arelay controlling a servo-motor, should exert a repeat-back or return action on the relay to out oil the action of the servo-motor to prevent the latter from moving the control surface too far.

The method of repeat-back used in emergency control is preferably the same as that used in the normal automatic pilot.

One form'of the invention adapted for use as an auxiliary emergency control in conjunction with an automatic pilot of the general type disclosed in United States Patent 1,992,970 dated March 5, 1935 will now be described with reference to the accompanyin drawings in which:

Fig. 1 is a schematic diagram of automatic control arrangements for actuating one of the control surfaces of an aircraft to control the aircraft about one axis, inclusive of means according to the invention for automatically engaging the automatic control means in an emergency.

Fig. 2 is a view partly in section of a special form of control pendulum according to'the invention which may be used in the system of Fig. 1 "or in other types of control system that'need to employ a gravity-responsive controller.

Fig. 3 is a sectional view of the control pendulum of Fig. 2 taken on the line AA of Fig. 2.

Fig.4 is a front elevation, partly in section, of

the gyro-vertical used for stabilizing the craft exerts automatic control of the elevator and therefore of the attitude of the craft. The servomotor may be controlled solely from a displacement signal, but in Fig. 1 is shown as controlled from the combination of a displacement signal and a rate signal, the former being obtained from a vertical axis gyroscope or other standard of position and the latter from a rate-of-turn gyroscope. The control arrangements for exerting 'oontrol'eifects from the vertical axis gyroscope are generally in accordance with those illustrated and described in United States Patent 1,992,970 dated March 5, 1935, with modifications to allow of part control from the rate-of-turn gyroscope and to include special switch arrangements constitutin features of the present invention.

The vertical-axis controlling gyroscope '220 (Fig. 5) serves to stabilize a semicircular cut-off plate 8 about'a horizontal axis. 9 lying transversely in the craft and constituting one part of a two-part pick-oil" or controller, and aco-operating member 19 constituting the second part of said pick-01f is rotatably mounted about the same axis 9 and carries ports I I i 2 in the form of narrow rectangular slots which are normally half-covered by the straight edge of the semicircular cut-off plate 8. The ports ll, !2 are in communication with pipes I3, M respectively, through passages, not shown, which maintain such communication during any rotational displacements to which the member lfl'may be subjected. The pipes l3, l4 lead toports |5, H5 in rotary valve chambers I1, l8; as shown, the rotary elements I9, 29 of the valves have cut-away segments which normally put the ports I5, |6 into communication with ports 2|, 22 respectively, from which pipes 23, 24 lead to two compartments 25, 26 in a diaphragm chamber 28 separated by the diaphragm 21. The two compartments 25, 26 communicate with the atmosphere through very restricted openings 29, 33.

The gyroscope, the cut-01f plate 8 attached to it, and the co-operating ported member ID, are all located inside the instrument case (not shown) of the gyroscope, which is closed to the atmosphere and has its interior maintained at a low pressure by some form of suction pump, Consequently air is drawn in through the openings 29, 3|], through the compartments 2'5, 26, pipes 23, 24, |3, I4 and ports |2 into the interior of the casing of the gyroscope. When the aircraft is horizontal fore and aft, the ports H and I2 are equally open and equal volumes of air flow through them; consequently the pressures in the compartments 25, 26 on either side of the diaphragm 21 are equal and the diaphragm remains stationary. However, if the craft should pitch upwards, taking the ported member |0 with it, the disc 8 covers port H and uncovers port I2, thus upsetting the balance of the air flow through the ports. As a result the pressure in compartment 25 of the diaphragm chamber 28 increases while that in compartment 26 decreases; the diaphragm 2? therefore moves to the right.

To the diaphragm 21 is attached the piston rod 3| of a piston type relay valve 32. The pistons 33, 34 of this relay valve normally cover ports 35, 36 from which pipes 31, 38 lead to opposite ends of the servo-motor 'i. Hydraulic fluid under pressure is supplied to the relay valve through a pipe 39 and port 49 in the wall of the valve cylinder lying midway between the normal positions of the pistons 33, 34, and an exhaust pipe 4| is connected to ports 42, 43 in the Walls of the valve cylinder beyond the ends of the pistons 33, 34.

When the diaphragm 21 moves to the right as the result of an upward pitch of the craft it takes with it the pistons 33, 34, and oil under pressure is thereby admitted into the right-hand end of the servo-motor I through pipe 39, ports 49, 36, and pipe 38. Piston 6 of the servo-motor is consequently forced to the left expelling oil from the left-hand end of the servo-motor cylinder through pipe 31, ports 35, 42, and pipe 4| to the sump. The movement of the servo-motor to the left produces a downward deflection of the elevator by means of the cables 2, 3. This checks the upward pitch. Conversely, if the craft were to pitch downwards, the elevator would be displaced upwards to check the pitch movement.

The movement of the servo-motor 6, and consequently the movement of the elevator 4, in this automatic control system is limited by the fact that the servo-motor is connected to cables 44, 45, which are connected to a pulley 46. The shaft 41 of this pulley is connected through a differential 48 to a gear wheel 49 meshing with teeth on the ported member I0; it follows that movement of the servo-motor brings about a movement of the ported member ID. The connections are such that the ported member ID is caused to turn on the craft about the axis 9 until it resumes a position of alignment with the cut-off plate 8 attached to the gyroscope. In this way it is ensured that the elevator moves only through an angle proportional to the pitch of the craft.

By means of the differential 48 auxiliary control movements may be introduced. In the arrangement shown in Fig. 1 a control term proportional to the rate of pitch is introduced in this way. For this purpose a gyroscope is employed having a rotor 50 spinnin about a fore-an'd-aft axis in a gimbal ring 5|, which'is mounted by means of bearings 52, 52' for oscillation about a vertical axis. The casing 54 of the gyroscope is closed against the atmosphere and a vacuum is maintained inside it by means of a suitable suction pump. A nozzle (not shown) admits air through the walls of the instrument case to spin the rotor. Air is also admitted through the lid of the instrument casing by two passages 55, 56, on opposite sides of the vertical axis of support of the gimbal ring. The upstanding shaft 53 of the gimbal ring 5| passes through the lid of the casing and there are attached to it two cut-off plates 51, 53, the latter outside the instrument casing and the former inside. These cut-01f plates 51, 58, are similar to the cut-off plate 8 and are disposed with respect to the passages 55, 56, in the same manner as the cut-off plate 8 is disposed with respect to the ports l2. However, the two semicircular plates 51, 58 are arranged on opposite sides of the plane of the gimbal ring 5!, so that in plan view they form a complete circle. The passages 55, 56, are terminated at their upper ends by narrow rectangular ports 59, 60 and at their lower ends by similar ports 6|, 62. The result is that, if the gimbal ring 5| turns about the axis of its bearings 52, 52' in one direction, port 59 is closed and port 66 is opened, whereas port 6| is opened and port 62 is closed. Thus passage 55 is put into full communication with the interior of the instrument, and passage 56 is put into full communication with the atmosphere. If the gimbal ring 5| were to turn in the opposite direction, the reverse state of affairs would be obtained. The pressures in the passages 55, 56, are communicated through passages 63, 64, and pipes 65, 66, to a pair of bellows, so that the difference in pressure between the passages 55, 55, is made effective to move a rod 69 connecting these bellows. The pipe 65 is shown connected to one of a pair of oppositely acting bellows 67. The pipe 66 is connected to the opposite bellows, not shown. The rod 69 extending axially between the two bellows engages with a rod 70 connected to the gimbal ring shaft 53.

No centralising spring is employed on the gimbal ring 5|; nevertheless, as will be seen, the gyroscope acts as a rate-of-turn gyro. If the craft begins to turn about the axis to which the device is responsive (in this case the athwartship axis) the gimbal ring 5| begins to precess about its pivot axis, but this precessional movement is soon checked because it results in unbalancing the pressures in the passages 55, 56, and the consequent difierence of pressure in these passages is applied to the bellows 61, to prevent further movement of the gimbal ring. The parts are so proportioned that, during a continuous turn of the craft at any rate within the range of values for which the device is intended to be effective, the gimbal ring 5| can never turn far enough to ensure that the ports 59, 62, are completely closed and the ports 69, 6| are completely open, or vice-versa. It follows that the diiference of pressure developed in the pair of bellows 67, and therefore in the passages easeme- 55;: 58;: is automatically-regulated touequal the craft. 2 From this :it"fol-lows;that the differential signal pressure developed by-the: gyro is-more nearly proportional to the" rate of turn through;

a-large. variation in rate than would be the case if centralizing. springs were employed, because the precessional force developed by thegyro de-.

creasesvwhen the gyro is precessed through a sub stantial angle awayfrom its neutral position, i. e.,vthe force'is not truly linear in proportion to the angle of precession. The pressuredeveloped in-the'passages 55, 56," is 'also-appliedithrough pipes .H, 12 to a differential bellows 13,1 74',-to produce axial movement of a rod 18. Thismovement is applied through rack and pinion gearing 11, 'I8,to the differential'lltlr A centralising spring 19 acts on the rod l'lfiso that the movement of this rod is proportional to the difference ofpressure acting on the bellows l3,14, and-therefore to. the. rate of turn of th craft. This constructionpossesses the further advantage that the passages 65 and 68 which are. tapped-intothe main passages H and 'lzlleading from the pick-up ports to the.=main'bellows 13, 19; I28; I20; may be restricted, thereby introducingaldelay in the centralizing of the gyroscope; thus. causing a largersignalupon changeof rate than is finally reached at a steady rate, thus introducing an angular acceleration term;-

If desired anindicator can Ice-attached to the rod vl6 to indicate the rate of turn of the craft. Clearly also a turn-responsive gyroscope of the kind described may be used not only in the pres-- ent control system "but in connection with-any other control'isystem in which it is required to use a pressure or movement proportional to afunction of the rate of turn of a craft-or otherment and partly on rate-of displacement. As-

is well known a control of'this type -is advantageous in rapidlydamping out-any tendency of the craft to oscillate.

When it is desired to effect manual control of a the elevator from the control column I the pilot may turn the-valve cock-80, which is connected acrossathe supply pipes 3?,"331eading-to the It is'then possible for-the piston servo-motor -'l'. 6 of the servo-motor to be actuated fromthe control column I without any appreciableopposition by the oil in the servo-motor to movementsof the piston 5. In order to carry out the present invention an additional or-alternative by-pass valve 89 islprovided across the supplypipes 38 leading to: the servo-motor. As showmthis valve is'of the rotary type.- Itconsists of a cylinder containing a cylindrical rotary member'dl tors 82, 89,thesexsectors-beingin communication with each other b means of a passagegB l assing through thezrotarymemberg. The :supply ipipe: 31 communicates :with twov l diametrically; i op'positez;

The -system is therefore one in which con-- having two diametrically-opposite cut-away secmounted a control wheel 92.

ports .85, v86;an'd the pi: 38 communicates; with;

a second pairz-oftdiametrically opposite ports-81; 88; Inthe position shown in the drawings'the cuteaway: sectors 82; 83 'do' not interconnect the pairtof ports 85, 86, withlthe pair 81, 88, sothat therservo-motor isnot Icy-passed. However, it

can'be seen that if the rotary memberfil is turned through approximately 'it will-put the port. st into communication with port 81; and port SB into communication with port 88, thus serving to by-pass the servo-motor. Therotary member 8! is solid with-the shaft 89"of a rotary magnet 98 whose construction is somewhat similar to that ofa-DJC; motor. A'spring 9| acts on the shaft 89 to maintain the rotary valve member 8| in the angularposition shown. However, if the windings of the rotary magnet 99 are energised; theshaft turnsthrough 90 thus causing the valve 89" to by-pass the servo-motor.

At the heacl of the control column I there is On the underside of thiswheel there is mounted a ring 93 which has freedom of movement in a vertical direction through a small distance; the ring is spaced from ;the'whee1 92 through the full extent of this freeof -a number of'contacts 95 carried on the ring to make contact with a corresponding contact 96 carried on the underside of the Wheel 92. The contacts '95 are connected together so that the 1 gaps between the contacts 95"and thecorrespondingcontacts 98 can be considered to form a single contact gap which will be closed whenever'the pilot grasps the control wheel 92 at any point on which this camis mounted is turned by means ken and therefore the rotary" magnet 90' cannot be energisedp The automatic control'system is then completely efiective;

emergencm position; which 'in'practic xis done by the pilotwhenever. he suspects or becomes, aware of .the approach of hostile aircraft' or is 7. about to undertake acrobatic manoeuvres, contact.

Sa is made-with .the. result that the pilot has only to grasp the control wheel 92 to cause rotary magnet 98" to be energised and thus to ensure turns the by-passvalve to the position shown inthe drawings in whichthe servo-motor is nolonger lay-passed; the automatic control system" thereforeaat once becomes efiectivec- Itris clear that-iii .the pilot shouldsuddenly Howeven'if the emer gency switch 'lilt'ismoved-to the leftvhand, or;

9 become incapacitated, through enemy action or otherwise, the same sequence of events will take place; the pilot will release his grasp of the control wheel 92 and the automatic control system will take over control of the craft to fly it in whatever attitude had previously been set on the control gyroscope. The fact that the ring 93 is on the under-side of the control wheel 92 ensures that, even if the pilot were to fall for- Ward on to the control wheel 532, he could not thereby accidentally close the contacts 95, 96 to hold the automatic control system out of action.

Preferably it is arranged that a warning signal is given to other members of the crew whenever the pilot releases his grip of the control wheel 92 i. e. whenever the emergency automatic con trol system takes over control. For this purpose a warning device, such as a lamp I62, is connected in parallel with the windings of rotary magnet 98, so that it is energised when the solenoid is energised.

It is plain that the invention can be put into effect with any type of automatic control system. For example the automatic control system may be one in which the elevator is controlled from an instrument responsive to the air-speed of the craft instead of one responsive to the inclination and the rate of change of inclination of the craft as in the system of Fig. 1. Also the auxiliary rate-of-turn gyroscope 56, and the ports actuated from it may be omitted, so that the control becomes a pure inclination control.

However, the presence of the rate of turn gyroscope in the system has the advantage of 'ensur-' ing that, when the pilot releases the wheel 92 and the automatic control system takes over control, to swing the craft in most cases into a difierent attitude, the change to the new attitude does not take place too violently.

In most automatic control systems that use gyroscopes as controlling instruments the gyroscopes are apt to be seriously disturbed if the aircraft carries out manoeuvres in which it becomes inclined at a large angle to the horizontal, whether because the angular freedom of movement of the rotor case or gimbal ring of the gyroscope is limited or because at large angles of inclination of the aircraft the gyroscope virtually loses one of its degrees of freedom. As a result, the gyroscope ceases for a time to be a reliable reference for automatic control. If the automatic control system were to be engaged under conditions where the gyroscope had been disturbed, the craft would be automatically controlled to take up an inclined attitude instead of a horizontal one, which might be very dangerous. It is therefore arranged that the automatic control that is automatically brought into operation if the pilot becomes incapacitated is carried out from controlling instruments other than the gyroscopes used in normal automatic control. One such arrangement will now be described. It comprises, as shown in Fig. l, a pendulum I03 pivoted about an axis lu l lying transversely in the craft, which can be brought into operation, as an alternative to the vertical axis gyroscope, to control the elevator s. The pendulum I03 lies inside an enclosing casing Hi5 pivoted about the same axis lot as the pendulum; this casing is closed against the atmosphere and its interior is maintained at a low pressure by means of a suitable vacuum pump. The change-over from lum is brought about by the rotary valves I1, I8.

The'rotary elements [9, 2B, of these valves are mounted on a common shaft I06 which may be actuated from a control handle I01. In the normal position of this handle the rotary elements I9, 20, are in the positions shown in Fig. 1, but, if the handle I0? is turned through approximately to the left into the secondary control position, the rotary elements i9, 20, will take up positions in which the ports 2|, 22, leading to the diaphragm chamber 28 are put into communication with ports I88, I09 instead of into communication with ports l5, l6. Ports IE8, IE9, communicate via pipes H0, IH, with ports H2, H3 in the lower wall of the casing 15. The inner surface of this wall is in the form of a cylinder having as axis the axis E04 of rotation of the casing H15 and of the pendulum I03.

The lower part or bob H4 oi the pendulum ms extends over an arc of the interior cylindrical surface of the casing 15, and is of cylindrical form over this arc, so that a very small radial clearance exists between the bob H l of the pendulum and the inner surface of the casing, this clearance being substantially constant if the pendulum and casing turn relatively to each other about the axis I04. The arcuate length of the bob H4 is equal to the distance between the ports H2, H3, so that in the normal relative position of the pendulum and the casing the- .ports H2, H3 are both bisected by the knife edges that form the extremities of the arcuate extent of the bob H4.

The ports H2, H3, are thus related to the bob I M- of the pendulum I03 in the same manner.

as are the ports l I, I2 to the cut-oif plate 8 of the gyroscope. In the secondary control po sition of handle Ill'l the pressures in the two sides 25 and 26 of the diaphragm chamber 28 are therefore controlled by the inclination of the craft relative to the pendulum I03 in the same manner as, during normal control, they are controlled by the inclination of the craft relative to the gyroscope. In fact, the ported casing I55 acts as a pick-off member for the pendulum in the same way as the ported member I 0 acts as a pick-off member for the gyroscope.

It follows that by operation of the changeover valves I9, 20, by means of the handle ID! the pendulum becomes a secondary controlling instrument alternative to the gyroscope for automatically regulating the inclination of the craft. The control is exerted through the same relay arrangements (diaphragm 21 and relay valve 32) and through the same servo-motor 7 as are used in the primary automatic control system.

In the secondary control system it is desirable to ensure that the pick-off member I05 is caused to follow up the primary controlling instrument H13 in the same way as the pick-off member in follows up the cut-off plate 8 under the control of the repeat-back cables 44, 45. For this reason repeat-back cables H5, H6, connected to the servo-motor, are employed to turn pulley H! which is connected through differential H8 and gearing H9 to turn the casing I05 to follow the movements of the pendulum H13 relative to the-s craft. Also it is desirable to include in the sec ondary control system the rate-of-pitch term provided by the rate-of-turn gyroscope 50 in the control of the elevator. For this purpose the differential I I8 is made to serve the same purpose as differential 48; it superimposes in the followback connection from servo-motor l to the pendulum casing I05 a movement applied by a pair gees-inte of'bellows I28, I which respond to the differ enceof'pr'essure picked off frointhe rate-of-turn" gyroscope 5B. In this way a control term proportional to the rate-of-turn of the craft is introduced into the secondary control systemas well as into the normal control system.

Ina modification of the system shown in Fig. 1

to the gyroscope.

thetwo-handles IllI, IIll are linked together; as'

represented by the dash-dot line connecting handles ICII and I87, or are replaced by a single handle operating both of the shafts I80 and. H36. As before, when the handle is moved frorn'th'e normalto the emergency position the 'systein'is rendered ready to take over automatic control when the pilot releases his grasp of the control wheel 92, but in this modification th'e'control systent i e. the one in whichthe primary controlling instrument is the pendulum I03 and not the gyroe. v

In a further modification the change-over handle I0! is replaced by automatic means" for actuating the'shait HIE if the gyroscope of the ncrmal automatic control system should be dis-" turbed. In United'St'ates' Patent No. 2,280,116 dated Apr; 21, 1942 there is described'a gyro-horizon in which means are included-for automatically'centralising and caging the gyroscope if excessive inclination of the craft relative to thegyrt: scope should occur, such excessive inclination serving to operate an electric contact which energises a solenoid to cage the gyroscope, Such a gyroscope may be used as the controlling gyroscope'in an aut'omatic control system similar to Fig. 1, as'shown in Figs. 4. and 5. In Fig. 4 thegyro 229 is shown as universally mounted by means of gimbal ring ZIJI. which is pivoted fore and aft on thecraft and which pivotally supports the gyro casing 2I5 on transverse axis '2Il2; The roll controller about the fore and aft axis is not shown, being behind the gyroscope, but the pitch controller is shown as actuated from a bail 'or loop 263 pivoted on transverse axis 9 -9 parallel to and'normally in line with axis 292, the cutoff plate 8 being shown secured to the bail. A caging means is shown on the gyroscope in the form of a plurality of curved fingers 284 spaced about the vertical axis of the gyroscope and each pivoted on pivots 295, 2G6, 201 and 208, respec-'- tively. Links 299 connect the fingers so that they are all operated together, and one fingeris connected through connecting rod 2H1 to the core 2| I of a solenoid 2I2. The fingers cooperate with a pin 2I3 extendingdownwardly from the bot tom of the gyroscope, so that when the fingers are closed together, the pin is centralized, and the gyroscope locked in a normally vertical positioi'i with respect to the craft. An elect'rlc'cirouit" is arranged between the pin 2I'3 and the fingers" so that whenever the fingers contact the pin, caused by relative inclination of the gyroscope and craft, a circuit is closed through the solenoid which closes the fingers to cage the gyroscope. It can then be readily arranged that the contact that energises the caging solenoid 2I2should also shaft I 06.

andthe pilot releases his grasp of wheel 99 the normal automatic control system automatically takes over control to control the craft from the gyroscope unless the gyroscope has been disturbed through excessive inclination of the shaft, in which case the gyroscope becomes caged autoniatially'. Inthe'lattercase, or if the'g'yrosc'ate tom that takes overis always the secondarysys- I... I .i I energise another solenoid 2M or motor to rotate I v This has the advantage that when the handle I BI is put into the emergency position It is evident that, if desired, the rotary valve may be replaced by a valve of the piston type, in which case the rotary magnet device may be-replaced by'a solenoid plunger connected to actuate thepiston; similarly the rotary valves I9, 20 may be replaced by valves of iston type.

The" arrangements for controlling the ailerons are generally similar to those shown in Fig. 1 for controlling the elevator. However, the method of controlling the rudder involves some differences. In this arrangement, when the automatic control system takes over control the system operates to bring the rudder toa central position, i. e., the rudder/ In-ari alternative emergency control system the rudder may be'left free, or floating. To secure this result, the only by-pass valve provided for the rudder servo-motor is a manually operated one, cor'responding to the by-pass valve 88' so that the pilot has" to operate this valve to lay-pass the rudder servo-motor when he wishes to take manualcohtrol of the craft. -When the pilot releases his grasp of the control wheel 92, the rudder servo-motor then remains by-passed, whereas the elevator and ailerons are put under automatic control.

It is evident from the foregoingthat either two or Y three servo-motors 'must simultaneously be brought into emergency operation when the pilot releaseshis grasp of the control wheel 92. For

:this'reason the'by-pass valves 86 for the several servo-motors to'be brought'into operation are preferably interconnected so as to be operated simultaneously by the same electro-magnetic device 99. Similarly, the change-over pneumatic valves ll, I8, in-the air-pressure control lines leading 'to the different diaphragm chambers, such as 28, for controlling the craft about its different'principal axes, may be ganged together for operation by a single operating member such as the handle I 01-.

Figs. 2' and 3 illustrate a novel type of control pendulum which may be used to replace the control pendulum I03 in the system of Fig, 1. This control pendulum I25 is an inverted or overslung rigid pendulum; it is supported on pivots on an axis I28 ina follow-up support or casing I29, which is itself mounted 'for' rotation about the same axis I28 in a stationary outer casing I30. For this-purpose the inner follow-up casing I29 is provided with a shaft I34 having reduced ends or trunnions I 3-I, I 3| supported in bearings I32 and I33 in the stationary outer casing. The shaft'l34isolid with the inner casing I29, turns with a very small clearance inside a bushing I35 forming an extension of the outer casing I30.

The pendulum I25 is carried in a recess I36 in the'inner casing I29? it is provided with a bob I31 normally carried above the pivot axis I28, this bob having a very small freedom of movement between the faces or walls I38, I39 of the recess, so that" the pendulum has a very small freedom of angular'movement relative to the" casing I 29.

Itis" clear that the pendulum I25 is unstable, so

that, if it becomes inclined to the slightest extent in either direction from the vertical position shown in Fig. 3, it will fall over in that direction and rest against either the wall I38 or the wall I39,- thereby closing either the port I 40 in the wall I38 or-the-port' MI in the wall-l39. The portsIdIl; I4I are connected by channels I42,

13- l43, respectively, to axially separated ports I14, I45 on the surface of the shaft I34, which open into circumferential channels I46, Ml in the outer casing I30. Channels I46, I41 are connected to channels I48, I49 in the outer casing I30, which serve as the means by which a pressure-responsive device, such as the diaphragm chamber 28 of Fig. 1, may be connected to be operated by the pendulum; in other words, if the pendulum of Figs. 2 and 3 were to be used in the system of Fig. 1 to replace the pendulum I03, the pipes H0, I I I of Fig. 1 would be connected to the channels I48, I49. The interior, or follow-up, casing I29 is adapted to be driven round the axis I28 by means of a gear wheel lee secured to pivot shaft I3I' and adapted to be driven by a second gear I5I which thus corresponds to the gear I I9 of Fig. 1.

In operation, the interior of easing I30 is maintained at reduced pressure by means of a suitable vacuum pump, which may withdraw air through any suitable exhaust orifice, such as orifice I52. The air enters the arrangement through the channels I 28, 263 and passes into the interior casing I29 through the ports M4, Hill which are supplied from the circular channels I45, I l'i. The air then flows out of the interior casing I2 through the ports Hill, I l! into the outer casing 139, from which it is withdrawn through orifice I52 by means of the vacuum pump. Clearly the amounts of air flowing into the system through the two channels I48, hi9 will be determined by the extent to which the ports I ia I4! are closed by the bob of the pendulum. For example, if the pendulum falls over to the left, port I40 will be substantially closed and port MI will be opened; very little air will then flow in through the channel M8, whereas a considerable volume will flow through port I49. The pendulum thus serves to unbalance the air flow in the two channels I49, I49 in the same manner as the pendulum I93 of Fig. 1 serves to unbalance the air flow through the ports H2, H3. Clearly, therefore, the inverted pendulum I25 can be used to replace the pendulum I03 of Fig. 1. It should be noted that, when this is done, the follow-back connec tions H5, H6 from the elevator servo-motor I should be so connected as to turn the casing I29 in the direction to restore the pendulum I25 towards the vertical position.

The inverted pendulum I25 is used in Fig. 1 to control air ports to provide an air pressure signal for control purposes; such a pendulum can equally well be used for operating an electrical contact in an electrical control system. Positive control pendulums, such as are normally used in gravity-responsive control systems, have disadvantages, in that they tend to oscillate about their axis of support; this tends to produce a similar oscillation in the craft or other system controlled by the pendulum. Furthermore, in the case where the pendulum actuates electric contacts, the tendency of the pendulum to oscillate about its'pivot axis is apt to produce bad sparking at the contacts. When an inverted pendulum is used both these defects are avoided, as the pendulum is aperiodic.

The invention has so far been described with particular reference to an automatic pilot operating generally in accordance with the principles disclosed in United States Patent No. 1,992,- 9'70 dated March 5, 1935. It can also be used in association with other types of automatic pilot. For example, in United States Patents Nos. 2,210,- 917 dated Aug. 13, 1940 and 2,210,916 dated Aug.

I pick-off device at the gyroscope, are not employed. This is due to the fact that the relay valve is designed differently from the relay valve 32 of Fig. 1 so as to incorporate in itself the necessary means for limiting the movement of the servo-motor resulting from a pressure signal applied from the gyroscope or other controlling instrument. If the invention is applied to an automatic control system of the type shown in United States Patents Nos. 2,210,917 and 2,210,916

control may be transferred in an emergency in accordance with the invention to a control pendulum differing from that shown in Fig. 1, and the follow-back connections II5. IIB may be dispensed with. The modified control pendulum for this purpose may have its pick-ofi ports II2, I I3 skewed relative to the cut-off edges of the bob I 54 of the pendulum I03, so that, as the pendulum moves through progressively increasing angles relatively to the casing I95, one of the ports II2, IE3 is progressively opened to a greater extent, while the other is progressively shut off-at least up to a predetermined angle of displacement of the pendulum from its normal position relative to the casing. In this way the difference of pressure picked off from the pendulum can be made proportional to the tilt of the craft up to a prede termined limited angle, which is a satisfactory method of control in automatic control systems of the kind referred to.

What we claim is:

l. A system of control for aircraft comprising an automatic pilot having pendulous controlling means therefore and gyro-vertical primary controlling means, said gyro-vertical controlling means including a rotor frame, caging means operative when said aircraft departs from a selected attitude by more than a predetermined tilt for caging said frame, and means brought into action by operation of said caging means for transferring control of said automatic pilot from said gyro-vertical to said pendulous controlling means.

2. A system of control for aircraft comprising an automatic pilot having rugged, coarse controlling means therefor and delicate, sensitive primary controlling means normally movable relative to said pilot, protective means operative when said aircraft departs from a selected flight path by more than a predetermined angular deviation for locking said delicate, sensitive primary controlling means, and means for transferring control of said aircraft from said delicate controlling means to said rugged controlling means upon operation of said locking means.

3. A system of control for aircraft as claimed in claim in which said last-named means includes means automatically responsive to relative tilt of said craft and primary control means exceeding a predetermined norm for transferring control of said pilot from said delicate to said rugged controlling means.

4. A control system for aircraft comprising normally operative gyroscopic automatic piloting means, normally inoperative flight-levelling means for urging said aircraft to assume a predetermined attitude by movement about at least one axis of motion, and means operative upon relative tile between said gyroscope and aircraft of more than a predetermined angle for transferring control of said aircraft from said norl mally operative automatic piloting means to said normally inoperative flight-levelling means.

5. A control system for aircraftv comprising automatic piloting means including a gyro-vertical with a rotor frame and caging means operative when said aircraft departs from an attitude by more than a predetermined tilt for caging said frame, pendulousl controlled levelling means for urging said aircraft to assume a predetermined attitude about at least one axis of motion, and means brought into action by operation of said caging means for transferring control of said aircraft from said gyro-vertical to said levelling means.

6'. A system of control for controlling the attitude of aircraft, comprising automatic means for controlling said aircraft under abnormal flight conditions, said automatic means including a fluid-flow control device comprising a pivotal mounting, an overslung casing adjustable on said mounting, fluid conducting ports in said casing, and an overslung freely movable coaxially pivoted. pendulum within said casing operative to close one'of said ports when said overslung pendulum is displaced from an equilibrium position directly above said pivotal mounting.

7. In an automatic pilot for aircraft, a fluidflow control device comprising a pivotal mounting, an overslung casin adjustable on said mounting, fluid conducting ports in said casing, an overslung, freely movable coaxially pivoted pendulum within said casing operative to close one of said ports when said overslung pendulum is displaced from an equilibrium position directly above said pivotal mounting, and differential pressure means for controlling the attitude of the craft subject to the resultin variation in pressure at said ports.

8. In an automatic pilot for aircraft, a fluidflow control device comprising a pivotal mount ing, an overslung casing adjustable on said mounting, oppositely facing fluid-conducting ports in said casing, an overslung pendulum coaxially pivoted and freely movable within said casing, said pendulum having a portion free to swing on an are passing through the centers of the faces of said fluid-conducting ports and operative to close one of said ports when said pendulum is displaced from an equilibrium position directly above said pivotal mounting, and differential pressure means for controlling the attitude of the craft subject to the resulting variation in pressure at said ports.

9. In an automatic pilot for aircraft, a fluidflow control device comprising a pivotal mounting, an overslung casin adjustable on said mounting, oppositely facing fluid conducting ports in said casing, an overslung coaxially pivoted pendulum movable within limits set by said casing and operative to close one of said op positely facing fluid conductin ports when said pendulum is displaced from an equilibrium position directly above said pivotal mounting, and differential pressure means for controlling the attitude of the craft subject to the resulting variation in pressureat said ports.

10. In a crash preventing means for aircraft having both manual control and automatic pilot control including servo means operable about each axis of the craft, a directional gyroscope and rate-of-turn detecting means for normal azimuth control, and means for bringing the aircraft out of a spin, including means for throwing the rudder servo means under the control of said wrate-of-turn detecting means,

11. A, crash preventing means as claimedin:

and means at the gyro-vertical responsive to tilt;

of the craft beyond said range of operation of the gyro-vertical for transferring control of said pilot from said gyro-vertical to said emergency control means.

13. A control system for aircraft, comprisingan automatic pi-lot having a gyroscope and servo motor and adapted to maintain said craft in a horizontal attitude, emergency control means ineluding an alternative pendulous device and said servo motor for also maintaining saidrcraft in a horizontal attitude, a third controller of the manual type including a, changeover trip, said third controller being adapted, when grasped, to render both said automatic pilot and emergency control inoperative and to place said emergency control and servo motor in a standby condition, thereby rendering said craft responsive to said controller, and means responsive to release of said trip by said pilot, for transferring control of said craft to said emergency control means.

14. In an automatic pilot for aircraft, a standard of position, a two-part pick-off thereat for controlling the attitude of the craft about a major axis, an angular rate gyroscope, a pick-off thereat giving a signal responsive to the rate of turn of the craft about said axis and air pressure means responsive to the magnitude and direction of said signal for altering the relation of the parts of the pick-off at the standard of position.

15. In an automatic recovery pilot for aircraft, a directional gyroscope and rate-of-turn gyroscope for controlling the rudder to guide the craft in azimuth, a, gyro-vertical and a rate-of-turn gyroscope for governing the ailerons to control attitude of the craft in roll, a rate-of-turn gyroscope to govern the elevator to control the attitude of the craft in pitch in combination with said gyro-vertical, and emergency means for recovering the craft under unusual conditions, including means for severing the control of said directional gyroscope and said gyro-vertical but allowing all three rate-of-turn gyroscopes to remain in control of their respective control surfaces.

16. In an automatic recovery pilot for aircraft, a gyroscopio standard of position, a two-part pick-off thereat for controlling the attitude of the craft about a major'axis, an angular rate gyroscope, a pick-on thereat giving a signal responsive to the rate of turn of the craft about said axis, an auxiliary non-gyroscopic standard of position, a pick-01f thereat for alternatively control-ling the attitude of the craft about said major axis, and air pressure means responsive to the magnitude and direction Of said signal for altering the relation of the parts of said pick-oils at both the primary and auxiliary standards of position, whereb said rate-of-turn gyroscope acts to suppress turns regardless of which standard of positionis in control.-

17. A system of control for aircraft comprising,

manual means for moving a control surface of an aircraft under normal flight conditions, alternative fluid fiow automatic control means for moving said surface to urge said craft to follow a preselected flight path, a by-pass valve in said fluid flow means permitting automatic control, spring means normally biasing said by-pass to the closed position, said manual means having thereon means for opening said by-pass means which is brought into action by grasping said manual means thereby rendering said steering gear unresponsive to said automatic control means and easily responsive to said manual means, whereby upon release of said manual means the by-pass is closed and said automatic means assumes control of said surface.

18. A control system as claimed in claim 17, in which the fluid-flow automatic control means includes a primary gyroscopic controller, servo motors responsive to said primary controller, a rate-of-turn gyroscope responsive to the turning movements of said aircraft about a primary axis, resiliently-centralized differential pressure actuated means for deriving a damping displacement from said rate-of-turn gyroscope, means for deriving a repeat-back displacement from said servo motors, and means for applying both displacements to said primary controller.

19. An auto-recovery pilot for aircraft including automatic means for bringing the aircraft into a condition of level, straight flight regardless of heading or previous attitude, including angular rate responsive devices for limiting the rate of turn of the craft about each axis thereof, a manual controller including a changeover trip, said controller being adapted, when grasped, to control the flight of the aircraft about any axis, and means responsive to the release of said trip 18 for transferring the control of the craft entirely to said auto-recovery pilot, whereby the craft is brought at a safe rate to straight, level flight regardless of its previous flight conditions.

20. An auto recovery pilot as claimed in claim 19, having a warning indicator also brought into action by the release of said trip.

ROBERT HAYES NISBET. ARTHUR PHILIP GLENNY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,015,837 Regnard Jan. 30, 1912 1,137,519 Newburger Apr. 27, 1915 1,156,760 Curry Oct. 12, 1915 1,187,439 Macy June 13, 1916 1,203,221 Macy Oct. 31, 1916 1,866,596 Hendrickson July 12, 1932 1,896,805 Sperry et a1 Feb. 7, 1933 2,007,515 Wunsch et al. July 9, 1935 2,051,837 Fischel Aug. 25, 1936 2,086,916 Kormann July 13, 1937 2,144,614 Carlson Jan. 24, 1939 2,183,939 Moss Dec. 19, 1939 2,238,300 Zand et a1 Apr. 15, 1941 2,286,561 Meredith June 16, 1942 FOREIGN PATENTS Number Country Date 243,485 Germany Feb. 14, 1912 515,205 Great Britain Nov. 29, 1939 Certificate of Correction Patent No. 2,439,750. April 13, 1948. ROBERT HAYES NISBET ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 14, line 51, claim 2, for the Word pilot read aircraft; line 56, for aircraft read pilot; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 13th day of July, A. D. 1948.

THOMAS F. MURPHY,

Assistant Uommz'ssioner of Patents.

Certificate of Correction Patent No. 2,439,750. April 13, 1948. ROBERT HAYES NISBET ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 14, line 51, claim 2, for the word pilot read aircraft; line 56, for aircraft read pilot; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 13th day of July, A. D. 1948.

THOMAS F. MURPHY,

Assistant Uommissioner of Patents. 

